In the fields of deodorization, exhaust gas treatment, and the like, various adsorbent materials have so far been developed. Activated carbon is a representative example of these, and it has been used widely in various industries for the purpose of air cleaning, desulfurization, denitrification, or removal of harmful substances by making use of its excellent adsorption performance. In recent years, demand for nitrogen has been increasing, for example, in semiconductor manufacturing processes and the like. Such nitrogen is produced from air by using molecular sieving carbon according to the pressure swing adsorption process or temperature swing adsorption process. Molecular sieving carbon is also used for separation and purification of various gases such as purification of hydrogen from cracked methanol gas.
When a mixture of gases is separated according to the pressure swing adsorption process or temperature swing adsorption process, it is common practice to separate it based on the difference between the gases in equilibrium adsorption amount or rate of adsorption to molecular sieving carbon or zeolite used as a separation adsorbent material. When the mixture of gases is separated based on the difference in equilibrium adsorption amount, conventional adsorbent materials cannot selectively adsorb only the gas to be removed, and the separation coefficient decreases, making it inevitable that the size of the apparatus used increases. When the mixture of gases is separated into individual gases based on the difference in rate of adsorption, on the other hand, only the gas to be removed can be adsorbed, although it depends on the kind of gas. It is necessary, however, to alternately perform adsorption and desorption, and also in this case, the apparatus used should be larger.
On the other hand, a polymer metal complex has also been developed as an adsorbent material providing superior adsorption performance. The polymer metal complex has features including (1) large surface area and high porosity, (2) high designability, and (3) a change in dynamic structure when exposed to external stimulation. The polymer metal complex is expected to attain adsorption properties that known adsorbent materials do not have.
Patent Literature 1, for example, discloses a process for producing a metal complex comprising a central metal, an organic ligand having a carboxylate group, and a bridging ligand capable of bidentate binding to the central metal, the process comprising the step of adding an organic acid such as formic acid as a catalyst. However, in the process of Patent Literature 1, an organic acid is used as a catalyst, and a metal complex comprising an organic acid as a constituent element is not disclosed.